An in-depth understanding of how cells function at a molecular level is central to the modern day approach to the problems of heart disease, cancer prevention and treatment, and many other health problems. Cell membranes are of considerable interest in this regard in part because incorporated into the biological membranes are a large number of proteins essential to cellular function. Some of the proteins span the membrane, generating a lipid-protein interface. The objective of our research is to determine, using esr spin labeling techniques, the polar headgroup and fatty acid chain specificities of the lipid protein interactons in three ubiquitous transmembraneous enzymes, cytochrome oxidase, Na/K-ATPase and Ca2 ion-ATPase. Central to this effort is the synthesis of several new structurally well defined spin labeled lipids which are close structural analogues to important lipid components to biological membranes.